The present invention relates to die casting machines of the type having threaded tie bars, and in particular to a strain gauge arrangement therefor.
Die casting machines typically include four main tie bars which retain the various parts of the die casting machine together during injection of the die. During die injection, the tie bars are tensed severely, thereby causing longitudinal elongation or strain in the tie bars within elastic limits. It is preferred that the four tie bars be uniformly strained, so that the die halves are held squarely together during the locking and injection sequence.
In one type of die casting machine, such as that disclosed in U.S. Pat. No. 3,547,184, the ends of the tie bars are threaded to facilitate adjusting the same to insure uniform tensioning. It is very difficult to accurately determine the strain in tie bars which have threaded ends, since the length of that portion of the rod under tension is not constant, but varies as the mating adjustment nuts are tightened and loosened. Hence, the tension or stress in each of the tie rods must be recalculated each time the tie rods are adjusted. This is a time consuming and tedious task that is particularly difficult to carry out under manufacturing conditions.